CompatHelper: bump compat for Makie to 0.21, (keep existing compat)
This pull request changes the compat entry for the Makie
package from 0.20.1
to 0.20.1, 0.21
.
This keeps the compat entries for earlier versions.
Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.